The present invention relates to a low refrigerant detecting apparatus for refrigerators, e.g., automobile air conditioning systems.
With a refrigerator of the type which is not provided with any special protective means against the leakage of refrigerant, there is the danger of the refrigerator being operated with the insufficient refrigerant. The problem with this is that the lubricating oil of the compressor is retained, for example, in the receiver in the refrigerating cycle, thus causing burning of the compressor. Particularly, with a refrigerator of the type in which the evaporation pressure regulating valve is provided on the low pressure side, leakage of the refrigerant causes the regulating valve to close, thus further aggravating the problem.
To overcome this difficulty, an apparatus has been proposed in Utility Model Publication No. 48-35861 which was published on Oct. 27, 1973 in Japan and assigned to the same assignee as that of the present application. The apparatus includes a semiconductor device whose resistance is changed by its self-heating and which is positioned between the condenser and the expansion valve and immersed in the liquid refrigerant in the receiver which collects the refrigerant in liquid form, whereby when the quantity of the liquid refrigerant becomes less than a predetermined value, the semiconductor device comes out of the liquid refrigerant and the degree of its cooling decreases, thus causing its resistance value to change by an amount smaller than a predetermined value and thereby generating a signal.
With this apparatus, whenever the liquid refrigerant in the receiver is exhausted, it always results in the generation of a signal. This gives rises to a problem from a practical point of view in that such condition does not always mean the complete loss of the cooling capacity, and there are cases where the refrigerating system is rendered inoperative despite the fact that the refrigerating system still retains its cooling capacity.
Further, since the liquid level of the liquid refrigerant in the receiver is changed by the rotational speed of the compressor, the heat load related to the inlet temperature of the evaporator, etc., there is the danger of generating a warning signal irrespective of the excess and deficiency of the refrigerant in liquid form.